The present invention relates to semiconductor devices, and more particularly to light emitting diodes having a bond pad on an ohmic contact.
Light emitting diodes (or LEDs) are well known solid state electronic devices capable of generating light upon application of a sufficient voltage. Light emitting diodes generally comprise a p-n junction formed in an epitaxial layer deposited on a substrate such as sapphire, silicon, silicon carbide, gallium arsenide and the like. The wavelength distribution of the light generated by the LED depends on the material from which the p-n junction is fabricated and the structure of the thin epitaxial layers that comprise the active region of the device.
Commonly, an LED includes an n-type substrate, an n-type epitaxial region formed on the substrate and a p-type epitaxial region formed on the n-type epitaxial region. In order to facilitate the application of a voltage to the device, an anode ohmic contact is formed on a p-type region of the device (typically, an exposed p-type epitaxial layer) and a cathode ohmic contact must be formed on an n-type region of the device (such as the substrate or an exposed n-type epitaxial layer).
In order to bond a wire to an ohmic contact for connecting the device to an external circuit, it is known to form a bond pad on the ohmic contact metal stack. It is also known to protect the LED by depositing a layer of passivation over the entire exposed surface of the device. However, the passivation layer must be partially removed to permit the connection of a wire to the bond pad. Forming and patterning a bond pad and passivation layer may require multiple complicated and expensive photolithography steps which require precise mask alignment. Such steps are time-consuming and errors made during photolithography steps may reduce or harm the operating characteristics of the device, which may result in diminished yields or increased testing costs. Accordingly, it would be desirable to simplify the process of forming bond pads on LED ohmic contacts.